To meet the demand for higher integration density and operating speed of LSIs, the effort to reduce the pattern rule is in rapid progress. The wide-spreading flash memory market and the demand for increased storage capacities drive forward the miniaturization technology. As the advanced miniaturization technology, manufacturing of microelectronic devices at the 65-nm node by the ArF lithography has been implemented in a mass scale. Manufacturing of 45-nm node devices by the next generation ArF immersion lithography is approaching to the verge of high-volume application. The candidates for the next generation 32-nm node include ultra-high NA lens immersion lithography using a liquid having a higher refractive index than water in combination with a high refractive index lens and a high refractive index resist film, extreme ultraviolet (EUV) lithography of 13.5 nm wavelength, and double patterning version of the ArF lithography, on which active research efforts have been made.
With respect to high-energy radiation of very short wavelength such as EB or X-ray, hydrocarbons used in resist materials have little absorption. Then resist materials based on polyhydroxystyrene composed mainly of hydrocarbon are under consideration.
The exposure system for mask manufacturing made a transition from the laser beam exposure system to the EB exposure system to increase the accuracy of line width. Since a further size reduction became possible by increasing the accelerating voltage of the electron gun in the EB exposure system, the accelerating voltage increased from 10 kV to 30 kV and reached 50 kV in the current mainstream system, with a voltage of 100 kV being under investigation.
As the accelerating voltage increases, a lowering of sensitivity of resist film becomes of concern. As the accelerating voltage increases, the influence of forward scattering in a resist film becomes so reduced that the contrast of electron image writing energy is improved to ameliorate resolution and dimensional control. However, electrons can pass straightforward through the resist film so that the resist film becomes less sensitive. Since the mask exposure tool is designed for exposure by direct continuous writing, a lowering of sensitivity of resist film leads to an undesirably reduced throughput. Due to a need for higher sensitivity, chemically amplified resist compositions are studied.
As the feature size reduces, image blurs due to acid diffusion become a problem. To insure resolution for fine patterns with a size of 45 nm et seq., not only an improvement in dissolution contrast is important as previously reported, but control of acid diffusion is also important as reported in Non-Patent Document 1. Since chemically amplified resist compositions are designed such that sensitivity and contrast are enhanced by acid diffusion, an attempt to minimize acid diffusion by reducing the temperature and/or time of post-exposure bake (PEB) fails, resulting in drastic reductions of sensitivity and contrast.
A triangular tradeoff relationship among sensitivity, resolution, and edge roughness has been pointed out. Specifically, a resolution improvement requires to suppress acid diffusion whereas a short acid diffusion distance leads to a loss of sensitivity.
The addition of an acid generator capable of generating a bulky acid is an effective means for suppressing acid diffusion. It was then proposed to incorporate in a polymer recurring units derived from an onium salt having a polymerizable unsaturated bond as acid generator. Patent Document 1 discloses a sulfonium salt having polymerizable unsaturated bond capable of generating a specific sulfonic acid and a similar iodonium salt. Patent Document 2 discloses a sulfonium salt having sulfonic acid directly attached to the backbone.
Besides the bulky acid generation, another approach for suppressing acid diffusion is also under study. Patent Documents 3 to 8 describe nitrogen-containing adhesive groups. The presence of an electron pair in nitrogen atom is effective for control of acid diffusion. However, nitrogen atom not only retards acid diffusion, but also inhibits acid catalyzed reaction. In such case, deprotection reaction does not take place, or even when deprotection reaction takes place, a slow reaction rate leads to a loss of contrast.